Yes. The 400 has more meat in the main bearing area, and the bearings are less prone to failure due to their smaller surface area. So you can run more RPM safely with a 3" journal than a 3.25" journal engine. All the blocks have the same high nickel content, at least from the '60's to the early '70's, as far as I know. The cheesy ones came out in the mid '70's.
__________________
Jeff 
|